Recently, there is a system devised to include a storage battery unit installed in buildings such as an ordinary house, an office building, or a factory, and supply power stored in the storage battery unit to an electrical device. The system charges the storage battery unit with the power including surplus power of a utility grid or power generated by a power-generating system using natural energy such as sunlight.
Such a system makes it possible to supply to the electrical device the power stored in its own storage battery unit, as well as the power from the utility grid. This contributes to reducing an electricity expense and CO2 emissions for each building.
There is a known technique devised to charge or discharge with power so that multiple storage batteries have their states of charge (SOC) stabilized in a predetermined range. Hence, the technique maximizes the charging and discharging power of each storage battery (See Patent Literature 1, for example).